Collect blood between 15 weeks, 0 days and 22 weeks, 6 days
Do not collect blood after performing amniocentesis, as that may lead to an artificially increased serum alpha-fetoprotein level and unreliable results
Centrifuge and aliquot within 2 hours of collection.
Minimum Sample Volume
0.5 mL
Required Information
Collection date is required
Stability
Refrigerated (preferred): 7 days
Ambient: 7 days
Frozen: 90 days
Unacceptable Specimen Conditions
Gross hemolysis
Limitations
Incorrect or incomplete information may significantly alter results
A screen-negative result does not guarantee the absence of fetal defects. A screen-positive result does not provide a diagnosis but indicates that further diagnostic testing should be considered (an unaffected fetus may have screenpositive result for unknown reasons). In fact, given the low prevalence of Down syndrome, the majority of women with a positive screen will not have a Down syndrome fetus
Maternal serum alpha-fetoprotein (AFP) should not be measured after amniocentesis because maternal-fetal transfusion may occur, which would falsely increase the serum AFP
In twin pregnancies, the risk for Down syndrome is approximated, using twin-adjusted medians. In cases where one twin has demised, results may be unreliable
Results are not available for triplets or higher-multiple pregnancies
Each center offering maternal serum screening to patients should establish a standard screening protocol, which provides pre- and post-screening education and appropriate follow-up for screen-positive results
In a small percentage of samples, there is potential for alkaline phosphatase associated positive interference in the Beckman Access uE3 assay. This potential interference does not appear to be related to the amount of alkaline phosphatase in the patient sample. A falsely elevated unconjugated estriol (uE3)test result can lead to inaccurately underestimating the relative risk of chromosomal abnormalities, such as trisomy 21 and 18
